Acquire the wake lock to ensure RoR isn't delayed

The server based RoR is time critical, and the secret has a life time
of 10 minutes by default. In one bug, we find the task scheduled by
RebootEscrowManager doesn't run until 13 minutes later. As a
precaution, hold the wake lock in RebootEscrowManager to make sure the
resume on reboot completes.

Bug: 191784420
Test: trigger a RoR
Change-Id: Ife17e279d28b73d22213188a795d0edab99d0818